Hypoxic drive

The hypoxic drive is a form of respiratory drive in which the body uses oxygen chemoreceptors instead of carbon dioxide receptors to regulate the respiratory cycle.

Normal respiration is driven mostly by the levels of carbon dioxide in the arteries, which are detected indirectly by central chemoreceptors when carbon dioxide crosses the blood–brain barrier, forming detectable Hydrogen ions, and directly by peripheral chemoreceptors, and very little by the oxygen levels. An increase in carbon dioxide will cause chemoreceptor reflexes to trigger an increase in ventilation. Hypoxic drive accounts normally for 10% of the total drive to breathe. This increases as the PaO₂ drops to 70 torr and below, while hypoxic drive is no longer active when PaO₂ exceeds 170 torr. The hypoxic drive is so weak that unconsciousness will develop before respiratory distress is noted and is therefore a risk for pilots flying at high altitudes. For this reason, supplemental oxygen is required by Federal Aviation Regulations for pilots flying above about 12,500 feet altitude in unpressurized airplanes.